With increasing development of networking techniques, various Internet Protocol (hereinafter, IP) terminal devices such as IP phones, wireless access points or network video recorders become more and more popular.
As known, each of the IP terminal devices should be driven by electric power. However, if each of the IP terminal devices is equipped with a power cable, the wiring and connections of the power cables should be taken into consideration. That is, the use of the power cable is not convenient.
As the number of the IP terminal devices increases, the wiring process becomes more complicated because of the power requirements. For solving the above drawbacks, a power over Ethernet (hereinafter, POE) technique has been disclosed.
The POE technique can be used to transmit DC electric power to the IP terminal devices while transmitting data based on the Ethernet cabling architecture.
FIG. 1 is schematic functional block diagram illustrating the architecture of a conventional POE system. As shown in FIG. 1, the POE system 10 includes a power sourcing equipment (hereinafter, PSE) 11 and a powered device (hereinafter, PD) 13. For example, the powered device 13 is a general IP terminal device. The power sourcing equipment 11 is used for providing DC electric power to the powered device 13.
According to the power level, the power sourcing equipment 11 is usually classified into two types. In particular, the power sourcing equipment 11 complying with the IEEE 802.3af-2003 standard (also referred as an AF type) can provide 12.95 W of power, and the power sourcing equipment 11 complying with the IEEE 802.3at-2009 standard (also referred as an AT type) can provide 25.5 W of power.
Correspondingly, the powered device 13 is classified into two types. The AF type powered device 13 is operated in a relatively low power level mode, and the AT type powered device 13 is operated in a relatively high power level mode.
FIG. 2 is a table illustrating the relationship between the type of the power sourcing equipment and the type of the powered device. Each row indicates the type of the power sourcing equipment, and each column indicates the type of the powered device. In this table, an AF type power sourcing equipment and an AT type power sourcing equipment cooperate with an AF type powered device and an AT type powered device. Consequently, four powering situations are provided.
In a first situation, the AF type powered device and the AF type power sourcing equipment are included in the POE system. Since the power level provided by the power sourcing equipment and the power level required for the powered device are substantially identical, the powered device can be normally operated.
In a second situation, the AF type powered device and the AT type power sourcing equipment are included in the POE system. Since the power level provided by the power sourcing equipment is higher than the power level required for the powered device, the powered device can be normally operated.
In a third situation, the AT type powered device and the AF type power sourcing equipment are included in the POE system. Under this circumstance, the power level provided by the power sourcing equipment is lower than the power level required for the powered device. Since the power level provided by the power sourcing equipment is insufficient, the AT type powered device is possibly unable to be powered on, or repeatedly powered on and off, or suffered from power interruption in the usage state. That is, the powered device is abnormally operated.
In a fourth situation, the AT type powered device and the AT type power sourcing equipment are included in the POE system. Since the power level provided by the power sourcing equipment and the power level required for the powered device are substantially identical, the powered device can be normally operated.
From the above discussions about the conventional POE system, if the power level provided by the power sourcing equipment is lower than the power level required for the powered device, the powered device fails to be normally operated.